Field of the Invention
The present invention relates to satellite-based global telecommunications networks and more particularly to pro-active message acknowledgement collection for improved downlink performance over reliable transport media in satellite-based global telecommunications networks.
Description of the Related Art
With the development of a global economy, commercial satellite-based global telecommunications networks have been developed. These networks typically provide both voice (telephone) and data link (messaging) services. One of the first of such networks has been operated by Iridium LLC since Nov. 1, 1998. The international aviation community has been using the Iridium global satellite network to provide worldwide voice and data services between airlines, air traffic control centers, and aircraft.
The data link services of the Iridium satellite network can be either circuit-switched, using the voice system to set up a dial-up data link, or message-switched, using either the Short message Service (SMS) or the Short Burst Data (SBD) techniques. The international aviation community has selected the SBD service to build the satellite-based extension of the worldwide Aircraft Communications Addressing and Reporting System (ACARS). As this service matured and operational data became available on data link performance over Iridium SBD, some issues became apparent.
ACARS has been originally developed with unreliable transport media in mind. Traditional broadcast radio on Very High Frequency (VHF) radio bands by itself does not guarantee the correct and complete reception of any broadcast message. Therefore, ACARS implemented a two-phase message protocol, where each sent message must be individually acknowledged by a specific response. When this protocol was implemented on the reliable transport media of the Iridium SBD system, the same send-response mechanism was used. Under certain conditions, the selected implementation leads to sub-optimal performance of the overall data link. In particular, successfully transmitted messages may remain unacknowledged due to a peculiarity in the Iridium SBD signaling system. The current implementation of the ACARS-over-Iridium-SBD system does not handle this anomaly gracefully and reverts to the backup approach of re-sending the message after 180 seconds. During this waiting time, the complete data link is blocked. The present invention offers a solution to this data link blocking that (a) offers a significant improvement of the existing ACARS-over-Iridium-SBD performance, (b) offers a less costly alternative to the 180 second re-send approach, and (c) does not need any change in existing satellite or ground equipment, while allowing existing airborne equipment to remain unchanged at the operator's discretion.